@St Ts The boss also has a split soul. First the original soul, then the reincarnation which is the boss and the vengeful spirit which was summoned by muni(the colleague) i think none of the characters are truly aware of what's going on. You can usually tell them apart by their eyes. The young master/summoned spirit has yellow eyes. The original body has brownish eyes. What I forgot to mention was that the young master, from the old era who loved muni went mad essentially because muni fell into an unconscious state. He tried to wake him up by any means necessary and inserted something in his body which made his(muni's) soul split. That's why the reincarnationMC) is incomplete. Vengeful spirits are beings that get created when the person has an unfulfilled desire. Muni's spirit(the colleague) wished to be with the young master. The boss spirit( the young master) wished to be with muni aswell. Since he couldn't fulfill his wish, he prayed to be reincarnated with muni, however muni's soul was already split and thus he's incomplete which is why he(the boss/young master)was punished by having his own soul split aswell. Hope this helps.
